1. Field of the Invention
The present invention relates generally to micro-mirrors of the type typically known as micro-electro-mechanical systems (MEMS) mirrors, and particularly to MEMS mirrors useful for controllably directing optical beams within an optical switch.
2. Technical Background
An emerging optical switching technology employs MEMS mirrors, moveable in at least two degrees of freedom, to steer optical beams within an optical switch. Within the switch, an incoming signal formed into an optical beam propagates to a first moveable mirror. By controllably positioning the first moveable mirror, the beam is directed to a selected second moveable mirror. The second moveable mirror is also controllably positioned, so as to receive the beam from the first mirror and reflect it to an optical beam receiver. The receiver may take various forms, such as, for example, a photodetector, or coupling optics for coupling the beam into a waveguide, or any other light-responsive or light-conducting devices useful for receiving an optical signal beam. Such an optical switch may also be bi-directional, in that the receiver may operate both as a receiver and as a source of an optical beam from an incoming signal, such as in the case of a receiver in the form of a waveguide plus coupling optics. A large-scale, low-loss optical cross connect may be formed by providing a plurality of such moveable mirrors, each with an optical view of some or all of the others.
MEMS devices are fabricated using materials and processes similar to those employed in integrated circuit fabrication. Such techniques allow simultaneous fabrication of many small mechanical or electromechanical devices on (or in) a single substrate. This simultaneous fabrication capability provides cost advantages for producing mirrors for use in an optical switch of the type described above.
The MEMS mirrors typically suggested for use in such optical switches each include some type of gimbal arrangement and two pairs of hinges. Each pair of hinges provides one degree of freedom of motion, so that both pairs together can provide the desired degree of freedom of motion for a mirror. While mirrors with gimbal arrangements of this type have been fabricated, the fabrication process is sometimes difficult, and the gimbal structure itself is complex and occupies a significant area on the MEMS substrate.
One aspect of the present invention is a moveable micromirror including a supporting structure, a flexible post extending from the supporting structure, and a table extending radially from the end of the post along a plane generally perpendicular to the post, the table having a reflective surface facing away from the supporting structure. The post, desirably formed of single-crystal silicon, is dimensioned to be sufficiently flexible to allow the reflective surface to be selectively moveable and positionable, with at least two degrees of freedom, when urged by a suitable actuating force.
In another aspect, the present invention includes a method of making an array of moveable micromirrors by deep etching a silicon substrate so as to form posts surrounded by trenches, etching back the surface of the substrate around the posts so as to allow the posts to protrude beyond the surface of the substrate, and affixing a table with a reflective surface thereon to the tops of a plurality of the posts. Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.